1. Field of the Invention
The present invention relates to a semiconductor chip, and more particularly, to a semiconductor chip including a redundant circuit having a fuse incorporated therein.
2. Description of the Related Art
As a method of selecting a redundant circuit in a semiconductor integrated circuit, there is employed a method of selecting the redundant circuit by fusing wiring by laser irradiation in many cases. A portion to be fused by laser irradiation (hereinafter, referred to as “fuse element”), which is used in the method, is formed of a conductive layer used as wiring in a semiconductor chip. An interlayer insulating film and a passivation film, which are formed above the fuse element, are to be etched into a predetermined thickness. A region to be opened by the etching (hereinafter, referred to as “fuse opening”) is applied with a laser beam, thereby cutting the fuse element formed below the fuse opening.
On the other hand, in a process of sucking a chip diced at the time of assembling the semiconductor chip, the diced semiconductor chip is mounted on a film placed on a push-up stage and is pushed up from a back surface side of the film. After that, the chip is sucked by vacuum suction with a collet made of metal. It is known that, in this case, the semiconductor chip is electrically charged due to frictional static electricity generated between the push-up stage and the film or due to peeling electrification generated between the film and the semiconductor chip, which results in generating electrostatic discharge when the semiconductor chip is brought into contact with the collet made of metal.
In a case where a collet contact portion is formed near a fuse region, the electrostatic discharge is generated through the fuse element and a circuit for selecting a redundant circuit connected to the fuse element, as a discharge path, in some cases. In this case, a current caused to flow through the circuit for selecting a redundant circuit due to the electrostatic discharge causes an operational failure of the circuit for selecting a redundant circuit in some cases. The operational failure occurs in the circuit for selecting a redundant circuit, for example, when a transient large current flows into the circuit to thereby fuse an element provided in the circuit, or when a high electric field is generated between a gate electrode and a semiconductor substrate in the circuit to thereby cause a gate oxide film to be damaged by the electrostatic discharge (for example, see “Electrostatic Discharge Failure Mechanisms of Semiconductor Devices” written by Yasuhiro Fukuda, Journal of the Institute of Electrostatics Japan, Vol. 29, No. 2, 2005, p. 106, and JP 11-163005 A).
In some conventional circuits for selecting a redundant circuit, a wiring layer is formed above the fuse element. However, the wiring layer is not positioned in a region of the fuse opening, and does not function as a protection element (for example, see JP 2005-166900 A, JP 2001-189385 A, JP 11-260922 A, JP 10-74838 A, and JP 62-84521 A).
In a case where the protection element for protecting the circuit against the discharge, which is generated through the fuse element and the circuit for selecting a redundant circuit connected to the fuse element, as a discharge path, is provided in the circuit for selecting a redundant circuit, it is necessary to provide the protection element having resistance equivalent to that of a charged device model (CDM) connected to a bonding pad so that a protection ability of the protection element is ensured. As a result, an area of the protection element becomes large. The area necessary for the protection element is a square region having sides of about 15 μm to 20 μm, for each protection element, while depending on device characteristics and the like.
Further, the protection element associated with the conventional fuse element is electrically connected between the fuse element and an internal circuit, or is connected in parallel with the internal circuit (for example, see JP 02-244740 A and JP 2006-073937 A). In addition, a conductive film is formed on an insulating film so as to be exposed to an inside of the opening of the fuse element, thereby preventing the electrostatic discharge from generating (for example, see JP 2006-080411 A).
FIG. 15 is a plan diagram showing regions in which components are formed on a semiconductor chip of a related art. As shown in FIG. 15, the electrostatic discharge reaches a fuse forming region 120 from a collet contact region 140 on a semiconductor chip 9 in some cases. FIG. 16 is a cross-sectional diagram showing a main part of the semiconductor chip of the related art. As shown in FIG. 16, an electrostatic discharge damage protection element is not provided in the conventional circuit for selecting a redundant circuit, so the current is caused to flow to the circuit for selecting a redundant circuit due to the electrostatic discharge. In FIGS. 15 and 16, the path for the electrostatic discharge is indicated by the bold dashed arrow. Accordingly, the operational failure occurs in the circuit for selecting a redundant circuit in some cases, for example, when a transient large current flows into the circuit along the fuse opening 17 to thereby fuse an element (for example, fuse element 21) provided in the circuit, or when a high electric field is generated between a gate electrode 25 and a semiconductor substrate 11 in the circuit to thereby cause the gate oxide film to be damaged by the electrostatic discharge.
As described above, the current caused to flow due to the electrostatic discharge generated at the time of assembling the semiconductor chip is discharged through the fuse element. As a result, there arises a problem in that a functional failure occurs in the semiconductor chip.